Rear speaker wire

Hello,
I am going to amp my front and rear factory speakers. I know this may lift an eye brow, but upon testing the factory sounds good when amped.
I plan on buying after market speakers, but I have other this to buy first
My question is: in the rear speakers how can I tell which side is POS and NEG? Does any one have a wire diagram?

Thanks for your time,
Tom

let me know the colors of the wires and then I can tell you. I just replaced mine but cant remeber the colors.

On the left I have yellow and brown
And on the right I have dark blue and light blue

yellow positive brown neg.
light blue pos. dark blue neg.

http://ccs.exl.info/carwires.html#GM

GENERAL MOTORS

P o w e r
Memory (+12v Constant) Orange
Ignition (+12v Switched) Yellow
Ground (-) Black
Illumination Gray
Dimmer Brown
Power Antenna Pink
S p e a k e r s
Right Front (+) Light Green
Right Front (-) Dark Green
Left Front (+) Tan
Left Front (-) Gray
Right Rear (+) Dark Blue
Right Rear (-) Light Blue
Left Rear (+) Brown
Left Rear (-) Yellow